Fairfax Oath ceremony and name changing,

If you live in Fairfax VA area, and you had an interview at USCIS Fairfax office please share your timeline with me,
My interview was in 30 Nov 2018 , I wanted to chang my name also.The officer said you should get your oath ceremony letter in next 3-4 weeks and I don’t get any letter yet.
How about your case? And when is next oath ceremony date? Is it just once in a month in fairfax?